1. Field of the Invention
The present invention concerns a machine tool having a tool spindle that receives a tool and has a vertically oriented spindle axis, and having a workpiece table on whose upper side is arranged at least one fixture for clamping in a workpiece to be machined with the tool, the tool spindle and workpiece table being displaceable relative to one another in a working region in which the workpiece is arranged.
2. Related Prior Art
A machine tool of this kind is known from DE 43 06 093 A1.
Commonly known machine tools generally have a workpiece table as well as a spindle head that carries the tool spindle and is displaceable relative to the workpiece table in three mutually orthogonal directions. It is also known to implement one or more of the orthogonal displacement directions by movement of the workpiece table.
Machine tools of this kind having vertical-axis tool spindles are used for material-removing machining of-among others-bulky and in some cases very heavy objects that are clamped onto the upper side of the workpiece table by way of a "fixture." Depending on the application and field of use, various cutting, cooling, and/or flushing fluids --referred to hereinafter generally as "coolants"--are used to cool the tool being used, to improve the cutting effect, and to remove the chips that are produced during machining.
The machine tools have an encapsulated working space in which machining of the workpiece is accomplished. This encapsulated working space allows a very high coolant flow, with which the chips can be flushed away from the working region, i.e. from the workpiece being machined, the tool that is in use, and the workpiece table and other parts of the machine tool.
It is known to transport the chips via "chip chutes" into collection containers that are arranged in the machine stand of the particular machine tool. The coolant involved is aspirated or pumped off in the machine stand and reprocessed --in particular, filtered and in some cases also chemically purified --for further use.
Despite reprocessing, with these machine tools each machining operation on a workpiece is associated with a certain coolant loss, which is perceived as disadvantageous. A further disadvantage arises from the need for "reprocessing" of the used coolant, which requires design precautions and is associated with a certain energy consumption.
For reasons of cost and environmental protection, efforts are therefore being made to use as little coolant as possible in order to reduce both losses and the outlay involved in reprocessing.
At a lower coolant flow, however, there exists the risk that chips will stay adhered to various points in the working space of the machine tool, so that machine tools of this kind must often be "finish-cleaned" from inside. This is done in some cases by automatically blowing out the working space with compressed air, after a workpiece has been machined, to remove the adhering chips. It is also known to have these cleaning operations performed specifically by operating personnel.
Although it is possible in this fashion to reduce the coolant flow and thus the coolant loss entailed by the coolant flow, and to reduce costs for reprocessing, this advantage is canceled out by wage-intensive labor expenditure and additional design outlay for blow-cleaning with compressed air.
It has also been found in general that removal of the chips is nevertheless often unsatisfactory, so that in some cases finish-cleaning by hand is in fact necessary; this entails not only further wage costs, but also undesirable downtime for the machine tools designed in this fashion.
A further general advantage may be seen in the fact that the collected chips are mixed with coolant, so that laborious separation of the coolant is necessary prior to any reprocessing of the chips, e.g. in the manufacture of blanks.
In the machine tool known from the aforementioned DE 43 06 093 A1, two fixtures in which workpieces are alternatingly clamped and machined are arranged on the workpiece table. For this purpose, the working region is asymmetrically divided, by a spray shielding panel, into a loading side and a machining side; by rotating the workpiece table about its vertical axis, the loading side and machining side on its upper side can be transposed.
The spray shielding panel has a lower wall part that is rigidly attached to the workpiece table, and a pivotably mounted wall part whose underside rests loosely on the upper side of the rigid wall part and automatically rises and then descends again as the workpiece table is lifted and rotated.
With this machine tool as well, the aforementioned disadvantages occur in connection with the chips that are produced, which collect on the workpiece table and cannot be completely removed therefrom even by a very large coolant flow; finish-cleaning by hand is therefore necessary, this being performed whenever a machined workpiece is replaced, on the loading side, with a workpiece that has yet to be machined.